Clarify add pieces and create set can be made concurrently

[hugomrdias]

its not clear in our docs and code comments that our nonces (and clientDataSetId) are not required to be sequential and thus making ppl (and llms) believe these transactions need to be made sequentially.

llms find this bit particularly confusing

synapse-sdk/packages/synapse-sdk/src/storage/context.ts

Lines 131 to 149 in 783ac4e

	/**
	* Get the client data set nonce ("clientDataSetId"), either from cache or by fetching from the chain
	* @returns The client data set nonce
	* @throws Error if data set nonce is not set
	*/
	private async getClientDataSetId(): Promise<bigint> {
	if (this._clientDataSetId !== undefined) {
	return this._clientDataSetId
	}
	if (this.dataSetId == null) {
	throw createError('StorageContext', 'getClientDataSetId', 'Data set not found')
	}
	const dataSetInfo = await this._warmStorageService.getDataSet({ dataSetId: this.dataSetId })
	if (dataSetInfo == null) {
	throw createError('StorageContext', 'getClientDataSetId', 'Data set not found')
	}
	this._clientDataSetId = dataSetInfo.clientDataSetId
	return this._clientDataSetId
	}

[BigLep]

Adding extra context while it's in my head: an anecdote where LLM got confused was for the Storacha to FOC migration tool.